Flux composition, connecting structure, and method for manufacturing the connecting structure

Abstract

Provided is a flux composition that can suppress the production of voids and increase conduction reliability in an obtained connection structure.　This flux composition includes an epoxy compound, and an organic acid or a neutralized product thereof, said organic acid including a releasable proton. After the flux composition has been heated at 250°C for 90 seconds, the condition of the heated product is a solid. When differential scanning calorimetry is performed by heating the flux composition in a nitrogen atmosphere from 30°C to 360°C at a temperature increase speed of 60°C / min, the temperature range of an exothermic peak includes 220°C, and the area of the exothermic peak in a temperature range of less than or equal to 220°C is less than 95% of the 100% total area of the exothermic peak.

Description

Technical Field

[0001] The present invention relates to a flux composition and the use of the flux composition. The present invention also relates to a connection structure using the above flux composition and a method for manufacturing a connection structure using the above flux composition.

Background Art

[0002] In recent years, with the miniaturization, weight reduction, and high functionality of electronic devices such as data servers, personal computers (PCs), and mobile terminals, the wiring pitch in printed wiring boards and the like has been becoming finer. Therefore, surface-mount packages such as ball grid arrays (BGAs) in which wiring extends directly under chips and ultra-small chip scale packages (CSPs) have attracted attention.

[0003] [[ID=1�]] However, in surface-mount packages such as BGAs, unlike conventional pin insertion-type packages, electrodes on the surface of the wiring board are connected by solder particles, so there is a problem that the adhesiveness is low and it is easily damaged by impacts such as dropping (low impact resistance).

[0004] Therefore, an underfill material may be filled and cured between the semiconductor chip and the semiconductor package substrate to reinforce the bonding portion.

[0005] Patent Document 1 below discloses a thermosetting resin composition for reinforcing electronic components having a viscosity of 5 Pa·s or less at 140°C. In this resin composition, the temperature corresponding to the top of the exothermic peak generated by the curing reaction is 150°C or higher and 170°C or lower, and the difference between the above temperature corresponding to the top and the temperature corresponding to half the height of the top in the rising portion of the exothermic peak is 20°C or lower.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

[0007] When an underfill material as described in Patent Document 1 is used as a encapsulant, it is possible to improve the adhesion between the semiconductor chip and the semiconductor package substrate, and to improve the impact resistance of the resulting connection structure (semiconductor package).

[0008] However, in the conventional production process for connection structures, after a reflow process (heating process) is performed to connect the electrodes, an underfill material is permeated and filled between the semiconductor chip and the semiconductor package substrate by capillary action, and another heating process is required to harden the underfill material. In other words, the conventional method of manufacturing a connection structure using underfill material, as described in Patent Document 1, has the problem of low productivity because the heating process must be performed twice.

[0009] Furthermore, when conventional underfill materials are used as the flux composition to fabricate connection structures, the flux composition hardens before the solder melts due to heating, preventing the solder from adequately wetting and spreading across the electrode surface. This can result in connection failures in the resulting connection structures. In other words, it is difficult to improve the conductivity reliability of the resulting connection structures with conventional flux compositions.

[0010] Furthermore, when a connection structure is fabricated using a conventional flux composition, heating during the reflow process can cause the flux composition to boil, generating bubbles and potentially creating voids in the resulting connection structure.

[0011] The object of the present invention is to provide a flux composition and a use of the flux composition that can suppress the generation of voids and improve conductivity reliability in the resulting connection structure. Another object of the present invention is to provide a connection structure using the above flux composition and a method for manufacturing the connection structure using the above flux composition. [Means for solving the problem]

[0012] This specification discloses the following flux compositions, uses of the flux compositions, connecting structures, and methods for manufacturing the connecting structures.

[0013] Item 1. A flux composition comprising an epoxy compound and an organic acid containing a freeable proton or a neutralized thereof, wherein the properties of the heated material at 250°C after heating the flux composition at 250°C for 90 seconds are solid, and when differential scanning calorimetry is performed on the flux composition while it is heated in a nitrogen atmosphere at a heating rate of 60°C / min from 30°C to 360°C, the exothermic peak temperature range includes 220°C, and the area of ​​the exothermic peak in the temperature range below 220°C is less than 95% of the total area of ​​the exothermic peak.

[0014] Item 2. The flux composition according to Item 1, further comprising a curing agent, wherein the curing agent comprises an acid anhydride and a phenol compound.

[0015] Item 3. The flux composition according to Item 2, wherein the amount of acid anhydride groups in the flux composition is 16 mol or more and 60 mol or less per 100 mol of epoxy groups in the flux composition.

[0016] Item 4. The flux composition according to any one of items 1 to 3, wherein the flux composition contains, in an amount of 2.0% by weight or less, an organic acid containing the liberable proton or its neutralized form.

[0017] Item 5. The flux composition according to any one of items 1 to 4, wherein the flux composition is a non-conductive flux composition.

[0018] Item 6. The flux composition according to any one of items 1 to 5, wherein the flux composition is a first-in underfill material used in a first-in underfill process.

[0019] Item 7. The flux composition according to any one of items 1 to 6, which is used in contact with a tin-silver-copper alloy solder.

[0020] Item 8. Use of any one of the flux compositions described in items 1 to 7 as a first-in underfill material in a first-in underfill process.

[0021] Item 9. Use of any one of the flux compositions described in items 1 to 7 as a flux for the surface of tin-silver-copper alloy solder.

[0022] Item 10. A connection structure comprising a first connection target member having a first electrode on its surface, a second connection target member having a second electrode on its surface, and a resin portion connecting the first connection target member and the second connection target member, wherein the first electrode comprises a first electrode body and solder particles on the surface of the first electrode body, the first electrode body and the second electrode are electrically connected, and the material of the resin portion is the flux composition described in any one of items 1 to 7.

[0023] Item 11. Using a first connection target member having a first electrode on its surface, the first electrode including a first electrode body and solder particles on the surface of the first electrode body, or a second connection target member having a second electrode on its surface, and using the flux composition according to any one of Items 1 to 7, a first arranging step of arranging the flux composition on the surface of the solder particles in the first connection target member or on the surface of the second electrode in the second connection target member; a second arranging step of arranging the first connection target member and the second connection target member such that the first electrode and the second electrode face each other; and a step of heating the solder particles and the flux composition to electrically connect the first electrode body and the second electrode and to form a resin part connecting the first connection target member and the second connection target member with the flux composition. A method for manufacturing a connection structure.

Effect of the Invention

[0024] The flux composition according to the present invention is a flux composition including an epoxy compound and an organic acid containing a dissociable proton or a neutralized product thereof. The property at 250°C of the heated product after heating the flux composition according to the present invention at 250°C for 90 seconds is solid. In the flux composition according to the present invention, when differential scanning calorimetry is performed by heating the flux composition from 30°C to 360°C at a heating rate of 60°C / min in a nitrogen atmosphere, the temperature region of the exothermic peak includes 220°C, and the area of the exothermic peak in the temperature region of 220°C or lower is less than 95% of the total area of the exothermic peak of 100%. In the flux composition according to the present invention, since the above configuration is provided, generation of voids can be suppressed and conduction reliability can be enhanced in the obtained connection structure.

Brief Description of the Drawings

[0025] [Figure 1] FIG. 1 is a cross-sectional view schematically showing a connection structure obtained using the flux composition according to an embodiment of the present invention. [Figure 2]Figure 2(a) is a cross-sectional view illustrating each step of an example of a method for manufacturing a connecting structure using a flux composition according to one embodiment of the present invention. [Figure 3] Figure 3(b1) is a cross-sectional view illustrating each step of an example of a method for manufacturing a connecting structure using a flux composition according to one embodiment of the present invention. [Figure 4] Figure 4(c) is a cross-sectional view illustrating each step of an example of a method for manufacturing a connecting structure using a flux composition according to one embodiment of the present invention. [Figure 5] Figure 5(d) is a cross-sectional view illustrating each step of an example of a method for manufacturing a connecting structure using a flux composition according to one embodiment of the present invention. [Figure 6] Figure 6(b2) is a cross-sectional view illustrating a modified example of a method for manufacturing a connecting structure using a flux composition according to one embodiment of the present invention. [Figure 7] Figure 7(b3) is a cross-sectional view illustrating a modified example of a method for manufacturing a connecting structure using a flux composition according to one embodiment of the present invention. [Figure 8] Figure 8(b4) is a cross-sectional view illustrating a modified example of a method for manufacturing a connecting structure using a flux composition according to one embodiment of the present invention. [Modes for carrying out the invention]

[0026] The details of the present invention will be described below.

[0027] (Flux composition) The flux composition according to the present invention is a flux composition comprising an epoxy compound and an organic acid containing a freeable proton or its neutralized product. The properties of the heated material after heating the flux composition according to the present invention at 250°C for 90 seconds are solid at 250°C. When differential scanning calorimetry is performed on the flux composition according to the present invention by heating it from 30°C to 360°C in a nitrogen atmosphere at a heating rate of 60°C / min, the temperature range of the exothermic peak includes 220°C, and the area of ​​the exothermic peak in the temperature range of 220°C or below is less than 95% of the total area of ​​the exothermic peak.

[0028] The above flux composition is thermocurable. The above flux composition has the property of curing upon heating.

[0029] In conventional methods, where a reflow process (heating process) is performed to connect electrodes, followed by sealing with an underfill material, the heating process is repeated twice—once for soldering and once for curing the underfill material—which results in low productivity.

[0030] The flux composition according to the present invention has the above configuration, so when manufacturing a connection structure using the flux composition, the solder can be melted and the electrodes joined together in a single heating step (reflow step), and the flux composition can be cured. For this reason, it is not necessary to perform the heating step twice. In other words, with the flux composition of the present invention, batch mounting is possible when manufacturing a connection structure, so productivity can be increased. Since it can be used as a flux composition that does not require cleaning, the flux composition according to the present invention can be used to manufacture connection structures with small distances between electrodes well (it is suitably used for manufacturing connection structures with small distances between electrodes). Furthermore, with semiconductor chips or semiconductor package substrates with large surface areas, penetration of general underfill materials is difficult or impossible. The flux composition according to the present invention can be used to manufacture connection structures using semiconductor chips or semiconductor package substrates with large surface areas well (it is suitably used for manufacturing connection structures using semiconductor chips or semiconductor package substrates with large surface areas). The flux composition according to the present invention is suitably used as a first-in underfill material. From the viewpoint of effectively exhibiting the effects of the present invention, the flux composition is preferably a first-in underfill material used in a first-in underfill process (use of the flux composition as a first-in underfill material used in a first-in underfill process). From the viewpoint of effectively exhibiting the effects of the present invention, the flux composition according to the present invention is preferably used in contact with solder (use of the flux composition as a flux on the surface of solder).

[0031] Furthermore, when a connection structure is fabricated using a conventional flux composition, the flux composition hardens before the solder melts due to heating, preventing the solder from adequately wetting and spreading across the electrode surface. This can result in connection failures in the resulting connection structure. In other words, it is difficult to improve the conductivity reliability of the resulting connection structure using conventional flux compositions.

[0032] Furthermore, when connecting structures are fabricated using conventional flux compositions, heating during the reflow process (heating process) can cause the flux composition to liquefy and boil, generating bubbles. As a result, voids may form in the resulting connecting structure. When voids form in the connecting structure, there is a problem in that the impact resistance of the connecting structure decreases. In other words, it is difficult to improve reflow resistance with conventional flux compositions.

[0033] The flux composition according to the present invention has the above configuration, which allows the solder to sufficiently wet and spread across the electrode surface, thereby reducing the connection resistance between the upper and lower electrodes in the resulting connection structure. As a result, the conductivity reliability of the resulting connection structure can be improved.

[0034] Furthermore, since the flux composition according to the present invention has the above-described configuration, it is possible to prevent the flux composition from boiling due to heating in the reflow process (heating process), and the generation of voids in the resulting connection structure can be suppressed. As a result, when the connection structure using the above-described flux composition is subjected to impact such as dropping, the probability of connection failure or other problems occurring and the connection structure failing can be reduced (the impact resistance of the resulting connection structure can be increased). In other words, the flux composition according to the present invention can improve reflow resistance.

[0035] The properties of the heated material after heating the above flux composition at 250°C for 90 seconds are solid at 250°C. With the above configuration, it is possible to suppress the incorporation of outgassing released from the substrate due to heating during the heating process, and to suppress the generation of voids in the resulting connection structure.

[0036] The properties of the heated material at 250°C after heating the above flux composition at 250°C for 90 seconds can be confirmed, for example, by the following method: Apply 0.05 g of the above flux composition to the surface of a copper plate (phosphorus deoxidized copper plate, "C1220" manufactured by Engineering Test Service Co., Ltd., 0.3 mm thick) placed on a glass plate ("Large Slide Glass" manufactured by Matsunami Glass Co., Ltd., 1.0 mm thick) to obtain a test specimen. Place the obtained test specimen on a hot plate heated to 250°C, with the glass plate side facing outwards. After heating the test specimen for 90 seconds, check the properties of the heated flux composition on the 250°C hot plate at 250°C by touching it with a bamboo skewer.

[0037] The above flux composition is heated in a nitrogen atmosphere at a heating rate of 60°C / min from 30°C to 360°C, and differential scanning calorimetry (DSC) is performed. In the above flux composition, the temperature range of the exothermic peak in the differential scanning calorimetry includes 220°C, and the area of ​​the exothermic peak in the temperature range below 220°C is less than 95% of the total area of ​​the exothermic peak. With the above configuration, the curing of the flux composition is prevented from being completed before the solder melts due to heating, and the solder can spread sufficiently on the surface of the electrode. As a result, the conductivity reliability of the resulting connection structure can be improved.

[0038] The differential scanning calorimetry (DSC) described above can be performed using the following method: Prepare a differential scanning calorimetry device. Place 5 mg of the flux composition in a dedicated aluminum pan (aluminum container). Place this dedicated aluminum pan and an empty aluminum pan (reference) in a heating unit and heat under conditions from 30°C to 360°C with a nitrogen flow rate of 50 mL / min and a heating rate of 60°C / min, and observe the reverse heat flow and non-reverse heat flow. The exothermic peak observed in the non-reverse heat flow is taken as the exothermic peak of the flux composition. Examples of the differential scanning calorimetry devices described above include the "EXSTAR DSC7020" manufactured by SII Corporation and the "DSC7020" manufactured by Hitachi High-Tech Science Corporation.

[0039] In the above flux composition, the temperature range of the exothermic peak in the differential scanning calorimetry includes 220°C. That is, the temperature range of the exothermic peak includes 220°C. In the above flux composition, the exothermic start temperature is 220°C or lower, and the exothermic end temperature is 220°C or higher. Furthermore, in the above flux composition, the reaction rate at 220°C of the above flux composition, as described later, is greater than 0% and less than or equal to 100%.

[0040] In this specification, the exothermic onset temperature refers to the temperature at which the amount of heat generated begins to rise from the baseline. Specifically, the exothermic onset temperature is defined as the temperature at which DDSC or DDDSC (obtained by differentiating DDSC with respect to temperature) becomes 0. In this specification, the exothermic termination temperature refers to the temperature at which the amount of heat generated decreases to 1% of the amount of heat generated at the exothermic peak after reaching the exothermic peak top.

[0041] In the differential scanning calorimetry described above, the area of ​​the exothermic peak in the temperature range of 220°C or below, out of 100% of the total area of ​​exothermic peaks, is defined as the reaction rate of the flux composition at 220°C. The reaction rate of the flux composition at 220°C is less than 95%. If the reaction rate of the flux composition at 220°C is less than 95%, the wettability of the solder will be low, and the conductivity reliability of the resulting connection structure will be low. The reaction rate of the flux composition at 220°C is preferably 1% or more, more preferably 5% or more, even more preferably 10% or more, particularly preferably 15% or more, preferably 94.5% or less, more preferably 94% or less, even more preferably 93% or less, even more preferably 85% or less, particularly preferably 80% or less, and most preferably 75% or less. If the reaction rate of the flux composition at 220°C is above the above lower limit, the release of outgassing due to boiling and thermal decomposition of the flux composition during the reflow process is suppressed, and the generation of voids can be further suppressed. If the reaction rate of the flux composition at 220°C is below the above upper limit, the wettability of the solder can be further improved, and the conductivity reliability of the resulting connection structure can be further enhanced.

[0042] From the viewpoint of further wetting and spreading the solder appropriately, the reaction rate of the flux composition at 220°C is preferably 70% or more, more preferably 75% or more, even more preferably 80% or more, particularly preferably 85% or more, and most preferably 90% or more.

[0043] The area of ​​the exothermic peak in the temperature range below 220°C (reaction rate of the flux composition at 220°C) within 100% of the total area of ​​the exothermic peaks mentioned above can be calculated, for example, by the method of numerical integration using spreadsheet software such as Excel or NEXTA standard analysis software ("Standard Analysis" manufactured by Hitachi High-Tech Corporation).

[0044] In the differential scanning calorimetry described above, the following methods can be used to adjust the temperature range of the exothermic peak, the exothermic start temperature, the exothermic peak top temperature, the exothermic end temperature, and the reaction rate of the flux composition at 220°C to the preferred range described above: a method for adjusting the type and combination of epoxy compounds; a method for adjusting the content of epoxy compounds; a method for adjusting the type and combination of curing agents described later; and a method for adjusting the content of curing agents.

[0045] Furthermore, the flux composition has good adhesive properties. The flux composition is suitably used as an adhesive. The flux composition is particularly suitable for bonding semiconductor chips to semiconductor package substrates (use of the flux composition for bonding semiconductor chips to semiconductor package substrates).

[0046] The above flux composition is suitably used to obtain a connection structure. The above flux composition is suitably used to obtain an electronic component. The above flux composition is suitably used for bonding and connecting a surface mount package to a wiring board (use of the above flux composition for bonding and connecting a surface mount package to a wiring board). Examples of the above surface mount package include BGA and CSP.

[0047] The above flux composition has good fluxing properties for solder. The above flux composition can effectively remove oxide films from the surface of electrodes and solder in the resulting connection structure. The solder to which the above flux composition can be applied is not particularly limited. The above solder is preferably a filler material with a liquidus temperature of 450°C or less, based on JIS Z3001: Welding Terminology. The above solder is preferably a metal (low melting point metal) with a melting point of 450°C or less. The above solder may be solder particles. The above solder particles are preferably metal particles (low melting point metal particles) with a melting point of 450°C or less. The above low melting point metal particles are particles containing a low melting point metal. The low melting point metal refers to a metal with a melting point of 450°C or less. The melting point of the low melting point metal is preferably 300°C or less, more preferably 260°C or less. The above solder is preferably a low melting point solder with a melting point of less than 250°C.

[0048] The low-melting-point metal constituting the solder described above is not particularly limited. The low-melting-point metal is preferably tin or an alloy containing tin. Examples of such alloys include tin-silver alloys, tin-copper alloys, tin-silver-copper alloys, tin-bismuth alloys, tin-zinc alloys, tin-indium alloys, and tin-antimony alloys. Due to their excellent wettability to electrodes, the low-melting-point metal is preferably tin, tin-silver alloys, tin-silver-copper alloys, tin-bismuth alloys, tin-indium alloys, and tin-antimony alloys, more preferably tin-silver-copper alloys, tin-bismuth alloys, tin-indium alloys, or tin-antimony alloys, and particularly preferably tin-silver-copper alloys.

[0049] From the viewpoint of effectively exhibiting the effects of the present invention, it is preferable that the flux composition be used in contact with the solder (use of the flux composition as a flux on the surface of the solder). The flux composition has particularly good fluxing properties with respect to tin-silver-copper alloy solder (SnAgCu solder). From the viewpoint of effectively exhibiting the effects of the present invention, it is preferable that the flux composition be used in contact with tin-silver-copper alloy solder (SnAgCu solder) (use of the flux composition as a flux on the surface of tin-silver-copper alloy solder (SnAgCu solder)). In other words, from the viewpoint of effectively exhibiting the effects of the present invention, it is preferable that the flux composition be used in the manufacture of a connection structure using tin-silver-copper alloy solder (use of the flux composition for the manufacture of a connection structure using tin-silver-copper alloy solder). From the viewpoint of effectively exhibiting the effects of the present invention, it is particularly preferable that the flux composition be used in contact with the Sn96.5Ag3.0Cu0.5 solder (use of the flux composition as a flux on the surface of the Sn96.5Ag3.0Cu0.5 solder).

[0050] From the viewpoint of further improving connection reliability, the melting point of the solder is preferably 100°C or higher, more preferably 150°C or higher, even more preferably 200°C or higher, preferably 400°C or lower, more preferably 350°C or lower, and even more preferably 300°C or lower.

[0051] The melting point of the above solder can be determined by differential scanning calorimetry (DSC). Examples of differential scanning calorimetry (DSC) equipment include the "EXSTAR DSC7020" manufactured by SII Corporation.

[0052] The flux composition described above is preferably non-conductive. The flux composition described above is preferably free of conductive substances. The flux composition described above is preferably free of conductive particles. The flux composition described above is preferably free of metal particles. The flux composition described above is preferably a non-conductive flux composition. When the flux composition satisfies these preferred embodiments, the conductivity reliability of the resulting connection structure can be further enhanced. In this specification, a non-conductive flux composition is defined as having a volume resistivity of 10 8 This shows a flux composition with a value of Ω·cm or greater.

[0053] The volume resistivity mentioned above is the volume resistivity at 20 kN. This volume resistivity can be measured using a resistivity meter (Mitsubishi Chemical Corporation's "Powder Resistivity Measurement System").

[0054] <Epoxy compounds> The above flux composition contains an epoxy compound. The epoxy compound is preferably a thermosetting compound. The epoxy compound is a compound having at least one epoxy group.

[0055] Examples of the epoxy compounds mentioned above include bixylenol-type epoxy compounds, bisphenol A-type epoxy compounds, bisphenol F-type epoxy compounds, bisphenol S-type epoxy compounds, phenol novolac-type epoxy compounds, biphenyl-type epoxy compounds, biphenyl novolac-type epoxy compounds, biphenol-type epoxy compounds, naphthalene-type epoxy compounds, fluorene-type epoxy compounds, phenol aralkyl-type epoxy compounds, naphthol aralkyl-type epoxy compounds, dicyclopentadiene-type epoxy compounds, anthracene-type epoxy compounds, epoxy compounds having an adamantane skeleton, epoxy compounds having a tricyclodecane skeleton, naphthylene ether-type epoxy compounds, and epoxy compounds having a triazine core as their skeleton. Only one of the epoxy compounds may be used, or two or more may be used in combination.

[0056] From the viewpoint of further improving the applicability of the above flux composition, the epoxy compound preferably contains a biphenyl-type epoxy compound, a bisphenol F-type epoxy compound, or an epoxy compound having a triazine core as its backbone, and more preferably contains a bisphenol F-type epoxy compound. The epoxy compound preferably contains a biphenyl-type epoxy compound, a bisphenol F-type epoxy compound, or an epoxy compound having a triazine core as its backbone, and more preferably a bisphenol F-type epoxy compound.

[0057] In 100% by weight of the above flux composition, the content of the epoxy compound is preferably 40.0% by weight or more, more preferably 45.0% by weight or more, even more preferably 50.0% by weight or more, preferably 70.0% by weight or less, more preferably 65.0% by weight or less, and even more preferably 60.0% by weight or less. When the content of the epoxy compound is above the lower limit and below the upper limit, the curability of the flux composition can be further enhanced, and the occurrence of voids in the resulting connection structure can be further suppressed.

[0058] <Organic acids or their neutralized products containing freeable protons> The above flux composition contains an organic acid containing a freeable proton or a neutralized product thereof. The above flux composition may contain an organic acid containing a freeable proton, may contain a neutralized product of an organic acid containing a freeable proton, or may contain both an organic acid containing a freeable proton and a neutralized product of an organic acid containing a freeable proton. In the above flux composition, the organic acid containing a freeable proton or a neutralized product thereof preferably acts as a curing accelerator or thickening inhibitor of the epoxy compound.

[0059] In this specification, a liberable proton refers to a proton with a pKa of 13 or less as measured in an aqueous solution at room temperature (for example, the three types of protons contained in phosphoric acid, protons contained in carboxylic acids, and protons contained in sulfonic acids). In this specification, a neutralized organic acid containing liberable protons refers to a neutralized organic acid capable of releasing free protons.

[0060] The above-mentioned organic acid containing liberable protons contains at least one liberable proton. The above-mentioned organic acid containing liberable protons or its neutralized product may contain one liberable proton, or it may contain two liberable protons. The above-mentioned organic acid containing liberable protons or its neutralized product may contain two or more liberable protons, or it may contain three or more liberable protons. The above-mentioned organic acid containing liberable protons or its neutralized product may contain 10 or fewer liberable protons, or it may contain 5 or fewer liberable protons, or it may contain 4 or fewer liberable protons. The above-mentioned organic acid containing liberable protons or its neutralized product may contain 3 or fewer liberable protons. From the viewpoint of improving storage stability and conductivity reliability, the flux composition preferably contains an organic acid containing one or two freeable protons or a neutralized thereof, and more preferably contains a neutralized organic acid containing one or two freeable protons. The range of the number of freeable protons can be set by appropriately selecting the lower limit and upper limit values ​​mentioned above.

[0061] Examples of organic acids containing liberable protons or their neutralized products include organophosphorus compounds, organic carboxylic acid compounds, organic sulfonic acid compounds, and organic thiol compounds. Only one of these organic acids containing liberable protons or their neutralized products may be used, or two or more may be used in combination.

[0062] From the viewpoint of further suppressing void formation and further improving conductivity reliability, the flux composition preferably contains an organophosphorus compound. From the viewpoint of improving conductivity reliability and suppressing void formation, the organic acid containing the liberable proton or its neutralized product preferably contains an organophosphorus compound.

[0063] Examples of the above-mentioned organophosphorus compounds include organophosphonium salts, organophosphoric acids, organophosphoric acid esters, organophosphonic acid esters, organophosphinic acids, and organophosphinic acid esters. The above-mentioned organophosphorus compounds may be used individually or in combination of two or more.

[0064] From the viewpoint of improving the conductivity reliability of the resulting connection structure, the organophosphorus compound preferably includes an organophosphonium salt, an organophosphoric acid, or an organophosphoric acid ester, and more preferably an organophosphonium salt.

[0065] Examples of the above-mentioned organic phosphonium salts include organic phosphonium salts composed of a phosphonium ion and its counterion.

[0066] From the viewpoint of improving the conductivity reliability of the resulting connection structure, the organic phosphonium salt is preferably methyltributylphosphonium dimethyl phosphate or tributylmethylphosphonium bis(2-ethylhexyl) phosphate. From the viewpoint of improving the conductivity reliability of the resulting connection structure, the organic phosphonium salt is more preferably methyltributylphosphonium dimethyl phosphate.

[0067] Examples of commercially available organic phosphonium salts include "Tetrabutylphosphonium bis(2-ethylhexyl)phosphate" manufactured by Johoku Chemical Industry Co., Ltd. and the "Hishikorin" series manufactured by Nippon Chemical Industrial Co., Ltd.

[0068] The above-mentioned organic phosphoric acid, organic phosphoric acid ester, organic phosphonic acid, organic phosphonic acid ester, organic phosphinic acid, and organic phosphinic acid ester are not particularly limited. Conventional known compounds or commercially available products can be used as the above-mentioned organic phosphoric acid, organic phosphoric acid ester, organic phosphonic acid, organic phosphonic acid ester, organic phosphinic acid, and organic phosphinic acid ester.

[0069] From the viewpoint of improving conductivity reliability and curability, it is preferable that the flux composition contains a neutralized organic acid containing the above-mentioned freeable protons.

[0070] In 100% by weight of the above flux composition, the content of the organic acid containing the freeable proton or its neutralized product is preferably 0.1% by weight or more, more preferably 0.2% by weight or more, even more preferably 0.5% by weight or more, preferably 5.0% by weight or less, more preferably 2.0% by weight or less, and even more preferably 1.0% by weight or less. When the content of the organic acid containing the freeable proton or its neutralized product is above the lower limit and below the upper limit, the generation of voids in the resulting connection structure can be further suppressed and the conductivity reliability can be further improved. In the case where the above flux composition contains both the organic acid containing the freeable proton and its neutralized product, the content of the organic acid containing the freeable proton or its neutralized product refers to the total content of the organic acid containing the freeable proton and its neutralized product.

[0071] In 100% by weight of the above flux composition, the content of the above organophosphorus compound is preferably 0.1% by weight or more, more preferably 0.2% by weight or more, even more preferably 0.5% by weight or more, preferably 5.0% by weight or less, more preferably 2.0% by weight or less, and even more preferably 1.0% by weight or less. When the content of the above organophosphorus compound is above the lower limit and below the upper limit, the generation of voids in the resulting connection structure can be further suppressed and the conductivity reliability can be further improved.

[0072] In 100% by weight of the above flux composition, the content of the above organic phosphonium salt is preferably 0.1% by weight or more, more preferably 0.2% by weight or more, even more preferably 0.5% by weight or more, preferably 5.0% by weight or less, more preferably 2.0% by weight or less, and even more preferably 1.0% by weight or less. When the content of the above organic phosphonium salt is above the lower limit and below the upper limit, the generation of voids in the resulting connection structure can be further suppressed and the conductivity reliability can be further improved.

[0073] The flux composition described above may or may not contain a curing accelerator other than the organic acid containing the freeable proton and its neutralized product (a curing accelerator different from both the organic acid containing the freeable proton and its neutralized product, hereinafter sometimes referred to as "other curing accelerator"). The flux composition may optionally contain the other curing accelerator. When the flux composition contains the other curing accelerator, the total content of the curing accelerator in 100% by weight of the flux composition is preferably 0.1% by weight or more, more preferably 0.2% by weight or more, even more preferably 0.3% by weight or more, preferably 4.0% by weight or less, more preferably 3.5% by weight or less, and even more preferably 3.0% by weight or less. When the total content of the curing accelerator is above the lower limit and below the upper limit, the generation of voids in the resulting connection structure can be further suppressed and the conductivity reliability can be further improved. The total content of the curing accelerator refers to the total content of the organic acid containing the freeable proton or its neutralized product and the other curing accelerator.

[0074] <Hardening agent> The above flux composition may or may not contain a curing agent. The above flux composition optionally contains the above curing agent. The above curing agent heat-cures the above epoxy compound. From the viewpoint of further improving the curability of the flux composition and further suppressing the generation of voids in the resulting connection structure, it is preferable that the above flux composition further contains a curing agent.

[0075] Examples of the curing agents include phenol compounds (phenol curing agents), active ester compounds, carbodiimide compounds (carbodiimide curing agents), amine compounds (amine curing agents), thiol compounds (thiol curing agents), phosphine compounds, dicyandiamides, and acid anhydrides. It is preferable that the curing agent has a functional group that can react with the epoxy group of the epoxy compound. The curing agent may be used alone or in combination of two or more.

[0076] From the viewpoint of preventing the flux composition from boiling due to heating in the reflow process and further suppressing the generation of voids in the resulting connection structure, the curing agent preferably contains an acid anhydride. From the viewpoint of controlling the curing rate of the flux composition and improving the conductivity reliability of the resulting connection structure, the curing agent preferably contains a phenol compound. From the viewpoint of further improving the conductivity reliability of the flux composition and further suppressing the generation of voids in the resulting connection structure, the curing agent more preferably contains both an acid anhydride and a phenol compound.

[0077] In 100% by weight of the above flux composition, the content of the above curing agent is preferably 30% by weight or more, more preferably 35% by weight or more, even more preferably 40% by weight or more, preferably 60% by weight or less, more preferably 55% by weight or less, and even more preferably 50% by weight or less. When the content of the above curing agent is above the lower limit and below the upper limit, the occurrence of voids in the resulting connection structure can be further suppressed and the conductivity reliability can be further improved.

[0078] The amount of curing agent functional groups in the flux composition relative to 100 mol of epoxy groups is preferably 50 mol or more, more preferably 60 mol or more, even more preferably 70 mol or more, preferably 110 mol or less, more preferably 100 mol or less, and even more preferably 90 mol or less. When the amount of curing agent functional groups in the flux composition relative to 100 mol of epoxy groups is above the lower limit and below the upper limit, the glass transition temperature of the cured product in the resulting connection structure can be effectively increased, further enhancing reliability. The curing agent functional groups are, for example, functional groups in the curing agent that act on the reaction of epoxy groups. Alternatively, the curing agent functional groups are, for example, functional groups in the curing agent that can react with epoxy groups. The curing agent functional groups are, for example, acid anhydride groups when the curing agent is an acid anhydride, and phenolic hydroxyl groups when the curing agent is a phenol compound. The amount of substance of the curing agent functional group described above is the amount of substance of the acid anhydride group when the curing agent is a type of acid anhydride, and the amount of substance of the phenolic hydroxyl group when the curing agent is a type of phenol compound. The amount of substance of the curing agent functional group described above is the sum of the amount of substance of the acid anhydride group and the amount of substance of the phenolic hydroxyl group when the curing agent is a type of acid anhydride and a phenol compound.

[0079] For example, the amount of curing agent functional groups in the flux composition relative to 100 moles of epoxy groups in the flux composition can be calculated from the functional group equivalents (g / eq) disclosed by the raw material manufacturer.

[0080] Furthermore, the amount of curing agent functional groups in the flux composition relative to 100 moles of epoxy groups in the flux composition can be measured, for example, by the following method: After dissolving the flux composition in a deuterated chloroform solution, 1 ¹H-NMR (JEOL's "JNM series") is measured, and the ratio of epoxy groups to curing agent functional groups is calculated from the obtained spectrum.

[0081] <<Acid anhydride>> The above flux composition may or may not contain an acid anhydride. The above flux composition optionally contains the above acid anhydride. The above acid anhydride causes the above epoxy compound to heat-cure. By using the above acid anhydride in combination with an organic acid containing a free proton or its neutralized product (especially an organophosphorus compound), the fluxing effect of the above flux composition can be significantly enhanced. The carboxylate ions produced by ring-opening of the acid anhydride group during the curing reaction exert fluxing properties. As a result, oxide films on the surface of electrodes and solder in the resulting connection structure can be effectively removed. Furthermore, by using the above acid anhydride in combination with the above phenol compound, the curability of the flux composition can be further enhanced, and boiling of the flux composition due to heating in the reflow process can be prevented. As a result, the generation of voids in the resulting connection structure can be further suppressed.

[0082] Examples of the above-mentioned acid anhydrides include phthalic acid anhydride, tetrahydrophthalic anhydride, trialkyltetrahydrophthalic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylbutenyltetrahydrophthalic anhydride, phthalic acid derivative anhydrides, maleic anhydride, nadic anhydride, methylnadic anhydride, glutaric anhydride, succinic anhydride, glycerin bistrimellitic anhydride monoacetate, and difunctional acid anhydrides such as ethylene glycol bistrimellitic anhydride, trifunctional acid anhydrides such as trimellitic anhydride, and tetrafunctional or more acid anhydrides such as pyromellitic anhydride, benzophenone tetracarboxylic anhydride, methylcyclohexenetetracarboxylic anhydride, and polyazelaic anhydride. The above-mentioned acid anhydrides may be used individually or in combination of two or more.

[0083] From the viewpoint of further improving the applicability of the above flux composition, the above acid anhydride preferably contains tetrahydrophthalic anhydride, hexahydrophthalic anhydride, or methylhexahydrophthalic anhydride, and more preferably contains methylhexahydrophthalic anhydride.

[0084] From the viewpoint of further improving the applicability of the above flux composition, it is preferable that the above acid anhydride is liquid at 25°C.

[0085] In 100% by weight of the above flux composition, the content of the above acid anhydride is preferably 1.0% by weight or more, more preferably 3.0% by weight or more, even more preferably 5.0% by weight or more, preferably 40% by weight or less, more preferably 38% by weight or less, and even more preferably 35% by weight or less. When the content of the above acid anhydride is above the lower limit and below the upper limit, the generation of voids in the resulting connection structure can be further suppressed and the conductivity reliability can be further improved. When the content of the above acid anhydride is below the upper limit, the wettability of the solder can be further improved.

[0086] The amount of acid anhydride groups in the flux composition relative to 100 mol of epoxy groups is preferably 10 mol or more, more preferably 16 mol or more, even more preferably 20 mol or more, preferably 70 mol or less, more preferably 65 mol or less, and even more preferably 60 mol or less. When the amount of acid anhydride groups in the flux composition relative to 100 mol of epoxy groups is above the lower limit and below the upper limit, the resulting connection structure can further suppress the generation of voids and further improve conductivity reliability. When the amount of acid anhydride groups in the flux composition is below the upper limit, the wettability of the solder can be further improved.

[0087] <<Phenol compounds>> The above flux composition may or may not contain a phenol compound. The above flux composition optionally contains the above phenol compound. The above phenol compound heat-cures the above epoxy compound. By using the above acid anhydride and the above phenol compound in combination, the flux composition can be prevented from boiling due to heating in the reflow process, the generation of voids in the resulting connection structure can be further suppressed, and the curability of the flux composition can be further enhanced, further suppressing the generation of voids in the resulting connection structure.

[0088] Examples of the phenol compounds mentioned above include novolac-type phenols, biphenyl-type phenols, naphthalene-type phenols, dicyclopentadiene-type phenols, aralkyl-type phenols, and dicyclopentadiene-type phenols.

[0089] Examples of commercially available phenol compounds include novolac-type phenol (DIC Corporation's "TD-2131"), novolac-type phenol (DIC Corporation's "TD-2091"), bisphenol (Gun-ei Chemical Industry Co., Ltd.'s "APG-LC"), biphenyl novolac-type phenol (Meiwa Chemical Co., Ltd.'s "MEH-7851"), aralkyl-type phenol (Meiwa Chemical Co., Ltd.'s "MEH-7800"), and phenols having an aminotriazine skeleton (DIC Corporation's "LA-1356" and "LA-3018-50P"). These phenol compounds may be used individually or in combination of two or more.

[0090] In 100% by weight of the above flux composition, the content of the above phenol compound is preferably 1.0% by weight or more, more preferably 3.0% by weight or more, even more preferably 5.0% by weight or more, preferably 35% by weight or less, more preferably 30% by weight or less, and even more preferably 25% by weight or less. When the content of the above phenol compound is above the lower limit and below the upper limit, the generation of voids in the resulting connection structure can be further suppressed and the conductivity reliability can be further improved.

[0091] In 100% by weight of the above flux composition, the total content of the above acid anhydride and the above phenol compound is preferably 20.0% by weight or more, more preferably 30.0% by weight or more, even more preferably 40.0% by weight or more, preferably 70.0% by weight or less, more preferably 60.0% by weight or less, and even more preferably 50.0% by weight or less. When the total content of the above acid anhydride and the above phenol compound is above the lower limit and below the upper limit, the generation of voids in the resulting connection structure can be further suppressed and the conductivity reliability can be further improved.

[0092] The sum of the amounts of acid anhydride groups and phenolic hydroxyl groups in the flux composition, relative to 100 mol of epoxy groups in the flux composition, is preferably 50 mol or more, more preferably 60 mol or more, even more preferably 70 mol or more, preferably 110 mol or less, more preferably 100 mol or less, and even more preferably 90 mol or less. When the sum of the amounts of acid anhydride groups and phenolic hydroxyl groups in the flux composition, relative to 100 mol of epoxy groups in the flux composition, is above the lower limit and below the upper limit, the resulting connection structure can effectively increase the glass transition temperature of the cured product and further improve conductivity reliability.

[0093] <Other ingredients> The above flux composition may optionally contain various additives such as fillers, bulking agents, softeners, plasticizers, thixotropes, leveling agents, polymerization catalysts, curing catalysts, colorants, antioxidants, heat stabilizers, light stabilizers, UV absorbers, lubricants, antistatic agents, and flame retardants.

[0094] (Connection structure and method for manufacturing the connection structure) The flux composition according to the present invention is suitably used to obtain a connecting structure.

[0095] The connection structure according to the present invention comprises a first connection target member having a first electrode on its surface, a second connection target member having a second electrode on its surface, and a resin portion connecting the first connection target member and the second connection target member. In the connection structure according to the present invention, the first electrode comprises a first electrode body and solder particles on the surface of the first electrode body. In the connection structure according to the present invention, the first electrode body and the second electrode are electrically connected. In the connection structure according to the present invention, the material of the resin portion is the flux composition described above.

[0096] In the method for manufacturing a connection structure according to the present invention, a first connection target member has a first electrode on its surface, the first electrode comprises a first electrode body and solder particles on the surface of the first electrode body, and a second connection target member has a second electrode on its surface. The method for manufacturing the connection structure comprises the following steps: (1) A first arrangement step of using the first connection target member or the second connection target member and using the flux composition described above to place the flux composition on the surface of the solder particles on the first connection target member or on the surface of the second electrode on the second connection target member. (2) A second arrangement step of arranging the first connection target member and the second connection target member so that the first electrode and the second electrode face each other. (3) A step of electrically connecting the first electrode body and the second electrode by heating the solder particles and the flux composition, and forming a resin portion connecting the first connection target member and the second connection target member with the flux composition.

[0097] In the pre-fill underfill method, the flux composition is placed on at least one surface of the first and second connection target members before the first and second connection target members are brought into contact with each other. The method for manufacturing a connection structure according to the present invention is a method for manufacturing a connection structure using the pre-fill underfill method.

[0098] In the manufacturing method of the above-described connection structure, the following arrangement methods may be employed. In the first arrangement step, a first connection target member having a first electrode on its surface, wherein the first electrode comprises a first electrode body and solder particles on the surface of the first electrode body, may be used, and the flux composition described above may be used to arrange the flux composition on the surface of the solder particles in the first connection target member. In the first arrangement step, a second connection target member having a second electrode on its surface, may be used, and the flux composition described above may be used to arrange the flux composition on the surface of the second electrode in the second connection target member.

[0099] In the method for manufacturing a connecting structure according to the present invention, in the first placement step, the flux composition may be placed by dispensing, by screen printing, by ejection using an inkjet device, or by dipping. From the viewpoint of further suppressing the generation of voids, it is preferable to place the flux composition by dispensing in the first placement step.

[0100] Conventional manufacturing methods for connection structures using underfill material require a reflow process (heating process) to connect electrodes, followed by the application of underfill material between the connection components via capillary action, and then another heating process to harden the underfill material. In other words, conventional manufacturing methods for connection structures using underfill material require two heating processes, resulting in low productivity. Furthermore, solder flash can occur in conventional connection structures using underfill material. Solder flash can lead to short circuits or open circuits.

[0101] The connection structure and method for manufacturing the connection structure according to the present invention use a specific flux composition, so that electrodes can be electrically connected and the flux composition can be cured in a single heating step (reflow step). Therefore, it is not necessary to perform the heating step twice. In other words, the connection structure and method for manufacturing the connection structure according to the present invention enable batch mounting, and as a result, productivity can be further increased. Furthermore, because the connection structure and method for manufacturing the connection structure according to the present invention use a specific flux composition, the solder in the solder particles can sufficiently wet and spread on the surface of the electrodes, and the connection resistance between the upper and lower electrodes in the connection structure can be reduced. As a result, the conductivity reliability of the connection structure can be improved. Furthermore, because the connection structure and method for manufacturing the connection structure according to the present invention use a specific flux composition, it is possible to prevent the flux composition from boiling due to heating in the reflow step (heating step), and the generation of voids in the connection structure can be suppressed. As a result, the probability of connection failure or other problems occurring and the connection structure failing when the connection structure is subjected to impact such as dropping can be reduced (impact resistance of the connection structure can be improved).

[0102] Specific embodiments of the present invention will be described below with reference to the drawings.

[0103] Figure 1 is a schematic cross-sectional view showing a connection structure obtained using a flux composition according to one embodiment of the present invention.

[0104] The connecting structure 1 shown in Figure 1 comprises a first connecting target member 2, a second connecting target member 3, and a resin part 4 connecting the first connecting target member 2 and the second connecting target member 3. The resin part 4 is formed from a flux composition 4Xa (see Figure 3(b1) (or Figure 6(b2) or Figure 7(b3) or Figure 8(b4)), Figure 4(c) and Figure 5(d)). The material of the resin part 4 is the flux composition 4Xa. The flux composition 4Xa contains an epoxy compound and an organic acid containing a freeable proton or its neutralized product. In this embodiment, the flux composition 4Xa is preferably in liquid form, and more preferably a solvent-free liquid.

[0105] The resin part 4 is a cured product formed by heat curing of the flux composition 4Xa.

[0106] The first connection target member 2 has a plurality of first electrodes on its surface (bottom surface). The first electrode comprises a first electrode body 2a and a solder portion 2B (solder particles) on the surface of the first electrode body 2a. The first electrode is a composite electrode of the first electrode body 2a and the solder portion 2B. The second connection target member 3 has a plurality of second electrodes 3a on its surface (top surface). In the connection structure 1, the first electrode body 2a and the second electrode 3a are electrically connected. In the connection structure 1, the first electrode body 2a and the second electrode 3a are electrically connected by the solder portion 2B.

[0107] As shown in Figure 1, in the connection structure 1, at least the portion of the solder particles in contact with the second electrode 3a melts between the first electrode body 2a and the second electrode 3a, and then the solder particles solidify to form a solder portion 2B. As a result, the contact area between the solder portion 2B and the second electrode 3a becomes larger.

[0108] Next, an example of a method for manufacturing a connecting structure will be specifically described using Figures 2(a), 3(b1) (or 6(b2), 7(b3), or 8(b4)), 4(c), and 5(d). Figures 2(a), 3(b1) (or 6(b2), 7(b3), or 8(b4)), 4(c), and 5(d) are cross-sectional views illustrating each step of an example of a method for manufacturing a connecting structure using a flux composition according to one embodiment of the present invention.

[0109] First, as shown in Figure 2(a), a first connection target member 2 having a first electrode on its surface (bottom surface) and a second connection target member 3 having a second electrode 3a on its surface (top surface) are prepared. The first electrode comprises a first electrode body 2a and solder particles 2b on the surface of the first electrode body 2a. A flux composition 4Xa is also prepared. The flux composition 4Xa comprises an epoxy compound and an organic acid containing a freeable proton or its neutralized product.

[0110] Next, as shown in Figure 3(b1), the flux composition 4Xa is placed on the surface of the solder particles 2b (first electrode) in the first connection target member 2 (first placement step). At this time, as shown in Figure 6(b2), the flux composition 4Xa may also be placed on the surface of the second electrode 3a in the second connection target member 3 (first placement step). That is, in the first placement step, the flux composition 4Xa is placed on the surface of the solder particles 2b in the first connection target member 2 or on the surface of the second electrode 3a in the second connection target member 3 by the dispensing method. The flux composition 4Xa is placed on the surface of the solder particles 2b in the first connection target member 2 or on the surface of the second electrode 3a in the second connection target member 3 using a dispenser.

[0111] In Figure 3(b1), the flux composition 4Xa is separately placed on each of the multiple solder particles 2b (first electrodes). As shown in Figure 7(b3), the flux composition 4Xa may be placed across the multiple solder particles 2b (first electrodes) (first placement step). In Figure 6(b2), the flux composition 4Xa is separately placed on each of the multiple second electrodes 3a. As shown in Figure 8(b4), the flux composition 4Xa may be placed across the multiple second electrodes 3a (first placement step). In the first placement step, the flux composition 4Xa may be placed on the surface of the second electrodes 3a of the second connection target member 3 by a dispensing method or the like, so as to span across the multiple second electrodes 3a.

[0112] The amount of flux composition placed on the surface of the solder particles is preferably such that it can fill the gap between the first member to be connected and the second member to be connected in the resulting connection structure.

[0113] Next, as shown in Figure 3(b1) (or Figure 6(b2) or Figure 7(b3) or Figure 8(b4)) and Figure 4(c), the first connection target member 2 and the second connection target member 3 are positioned so that the first electrode (first electrode body 2a and solder particles 2b) and the second electrode 3a face each other (second positioning step). The second connection target member 3 is positioned from the second electrode 3a side toward the first electrode side of the first connection target member 2. At this time, the first electrode body 2a and the second electrode 3a face each other.

[0114] Next, as shown in Figures 4(c) and 5(d), the solder particles 2b and the flux composition 4Xa are heated (third step). Preferably, the flux composition 4Xa is heated to a temperature above the melting temperature of the portion of the solder particles 2b that contacts the second electrode 3a. More preferably, the flux composition 4Xa is heated to a temperature above the curing temperature of the epoxy compound. This heating electrically connects the first electrode (first electrode body 2a and solder particles 2b or solder portion 2B) to the second electrode 3a. The flux composition 4Xa also undergoes thermal curing. As a result, as shown in Figure 5(d), the resin portion 4 connecting the first connection target member 2 and the second connection target member 3 is formed by the flux composition 4Xa. The resin portion 4 is formed by the thermal curing of the flux composition 4Xa. Furthermore, as shown in Figure 5(d), a solder portion 2B is formed by the solder particles 2b, and the first electrode body 2a and the second electrode 3a are electrically connected by the solder portion 2B.

[0115] The viscosity (ηmp) of the flux composition at the melting point of the solder particles is preferably 0.1 Pa·s or higher, more preferably 0.2 Pa·s or higher, preferably 50 Pa·s or lower, more preferably 10 Pa·s or lower, and even more preferably 1 Pa·s or lower. When the viscosity (ηmp) is above the lower limit and below the upper limit, the conductivity reliability of the resulting connection structure can be improved.

[0116] The viscosity (ηmp) can be measured, for example, using a Thermo Fisher Scientific HAAKE MARS III rheometer under the following conditions: frequency 2 Hz, heating rate 0.11 °C / sec, and measurement temperature range 25 °C to 200 °C (however, if the melting point of the solder particles exceeds 200 °C, the upper temperature limit will be the melting point of the solder particles). From the measurement results, the viscosity of the flux composition at the melting point (°C) of the solder particles can be evaluated.

[0117] In this way, the connection structure 1 shown in Figure 1 is obtained. Note that the second arrangement step and the third step may be performed consecutively. Alternatively, after performing the second arrangement step, the laminate of the first connection target member 2, the flux composition 4Xa, and the second connection target member 3 may be moved to the heating section and the third step may be performed. To perform the heating, the laminate may be placed on a heating member, or the laminate may be placed in a heated space.

[0118] The heating temperature in the third step is preferably 140°C or higher, more preferably 160°C or higher, preferably 450°C or lower, more preferably 250°C or lower, and even more preferably 200°C or lower. The heating temperature in the third step is preferably above the melting point of the solder particles. The heating temperature in the third step is preferably above the curing temperature of the epoxy compound. The heating temperature in the third step is preferably above the melting temperature of the portion of the solder particles that is in contact with the second electrode, and more preferably above the curing temperature of the epoxy compound.

[0119] Examples of heating methods in the third step described above include heating the entire laminate using a reflow oven or oven, and locally heating only the solder and resin parts of the laminate.

[0120] Examples of devices used for localized heating include hot plates, heat guns that apply hot air, soldering irons, and infrared heaters.

[0121] Furthermore, when heating locally with a hot plate, it is preferable to form the top surface of the hot plate with a metal that has high thermal conductivity directly beneath the soldered and resin parts, and with a material with low thermal conductivity, such as fluororesin, in other areas where heating is undesirable.

[0122] The thickness of the solder portion in the connecting structure is preferably 10 μm or more, more preferably 20 μm or more, preferably 100 μm or less, and more preferably 80 μm or less.

[0123] The thickness of the resin portion in the connecting structure is preferably 10 μm or more, more preferably 20 μm or more, preferably 100 μm or less, and more preferably 80 μm or less.

[0124] When the flux composition is a paste (liquid), it becomes easy to adjust the thickness of the resin portion by changing the amount of flux composition applied.

[0125] The first and second connection targets described above are not particularly limited. Specifically, the first and second connection targets include electronic components such as semiconductor chips, semiconductor packages, LED chips, LED packages, capacitors and diodes, as well as electronic components such as resin films, printed circuit boards, flexible printed circuit boards, flexible flat cables, rigid-flexible circuit boards, glass epoxy circuit boards and glass circuit boards. It is preferable that the first and second connection targets are electronic components.

[0126] Examples of electrodes provided on the above-mentioned connection target member include metal electrodes such as gold electrodes, nickel electrodes, tin electrodes, aluminum electrodes, copper electrodes, molybdenum electrodes, silver electrodes, SUS electrodes, and tungsten electrodes. When the above-mentioned connection target member is a flexible printed circuit board, the electrodes are preferably gold electrodes, nickel electrodes, tin electrodes, silver electrodes, or copper electrodes. When the above-mentioned connection target member is a glass substrate, the electrodes are preferably aluminum electrodes, copper electrodes, molybdenum electrodes, silver electrodes, or tungsten electrodes. In the case of aluminum electrodes, the electrodes may be made solely of aluminum, or they may be electrodes in which an aluminum layer is laminated on the surface of a metal oxide layer. Examples of materials for the metal oxide layer include indium oxide doped with a trivalent metal element and zinc oxide doped with a trivalent metal element. Examples of the trivalent metal element include Sn, Al, and Ga.

[0127] The solder described above is preferably a metal with a melting point of 450°C or less (low melting point metal). The solder particles described above are preferably metal particles with a melting point of 450°C or less (low melting point metal particles). The low melting point metal particles described above are particles containing a low melting point metal. The low melting point metal refers to a metal with a melting point of 450°C or less. The melting point of the low melting point metal is preferably 300°C or less, more preferably 260°C or less. The solder described above is preferably a low melting point solder with a melting point of less than 250°C.

[0128] The low-melting-point metal constituting the solder particles described above is not particularly limited. The low-melting-point metal is preferably tin or an alloy containing tin. Examples of such alloys include tin-silver alloys, tin-copper alloys, tin-silver-copper alloys, tin-bismuth alloys, tin-zinc alloys, tin-indium alloys, and tin-antimony alloys. Due to their excellent wettability to electrodes, the low-melting-point metal is preferably tin, tin-silver alloys, tin-silver-copper alloys, tin-bismuth alloys, tin-indium alloys, and tin-antimony alloys, and more preferably tin-silver-copper alloys, tin-bismuth alloys, tin-indium alloys, or tin-antimony alloys.

[0129] The solder particles described above are preferably filler materials with a liquidus temperature of 450°C or lower, based on JIS Z3001: Welding Terminology. Examples of the composition of the solder particles include metal compositions containing zinc, gold, silver, lead, copper, tin, bismuth, and indium. The solder particles are preferably lead-free and preferably contain tin, silver, and copper. The solder particles are preferably tin-silver-copper alloy solder particles.

[0130] To further enhance the bonding strength between the solder and the electrode, the solder particles may contain metals such as nickel, copper, antimony, aluminum, zinc, iron, gold, titanium, phosphorus, germanium, tellurium, cobalt, bismuth, manganese, chromium, molybdenum, and palladium. Furthermore, from the viewpoint of further enhancing the bonding strength between the solder and the electrode, it is preferable that the solder particles contain nickel, copper, antimony, aluminum, or zinc. From the viewpoint of further enhancing the bonding strength between the solder and the electrode, the content of these metals for enhancing bonding strength is preferably 0.0001% by weight or more, and preferably 1% by weight or less, out of 100% by weight of the metal contained in the solder particles.

[0131] From the viewpoint of further improving connection reliability, the melting point of the solder particles is preferably 100°C or higher, more preferably 150°C or higher, even more preferably 200°C or higher, preferably 400°C or lower, more preferably 350°C or lower, and even more preferably 300°C or lower.

[0132] The melting point of the solder particles mentioned above can be determined by differential scanning calorimetry (DSC). Examples of differential scanning calorimetry (DSC) equipment include the "EXSTAR DSC7020" manufactured by SII Corporation.

[0133] Furthermore, it is preferable that the solder particles contain tin. The tin content in the solder particles is preferably 30.0% by weight or more, more preferably 40.0% by weight or more, even more preferably 70.0% by weight or more, and particularly preferably 90.0% by weight or more. When the tin content in the solder particles is above the lower limit, the conductivity reliability and connection reliability of the connection structure can be further improved. There is no particular upper limit to the tin content in the solder particles. The tin content in the solder particles may be 99.9% by weight or less, 99.0% by weight or less, or 98.0% by weight or less.

[0134] The tin content can be measured using a high-frequency inductively coupled plasma atomic emission spectrometer (for example, Horiba's "ICP-AES") or an X-ray fluorescence analyzer (for example, Shimadzu's "EDX-800HS").

[0135] The present invention will be specifically described below with reference to examples and comparative examples. The present invention is not limited to the following examples.

[0136] The following materials were prepared.

[0137] Epoxy compounds: Bisphenol F type epoxy compound (DIC Corporation's "EXA-830CRP") Bixylenol-type epoxy compound (Mitsubishi Chemical Corporation's "YX-4000HK") Amine-based tetrafunctional epoxy compound (tetraglycidyldiaminodiphenylmethane, "ELM-434" manufactured by Sumitomo Chemical Co., Ltd.) Naphthalene-type epoxy compound (DIC Corporation's "HP-4710")

[0138] Hardener: Acid anhydride (a mixture of hexahydrophthalic anhydride and methylhexahydrophthalic anhydride, "Ricacid MH-700" manufactured by Shin Nippon Rika Co., Ltd.) Bisphenol compound (APG-LC, manufactured by Gun-ei Chemical Industry Co., Ltd.) Novolac-type phenolic compound (DIC Corporation's "TD-2131")

[0139] Curing accelerator (organic acid containing freeable protons or its neutralized form): Methyltributylphosphoniumdimethylphosphate (Hishicolin PX-4MP, manufactured by Nippon Chemical Industries, Ltd., number of free protons: 1) Phosphonium salt 1 (a compound represented by the following formula (1), number of free protons: 1) Phosphonium salt 2 (a compound represented by the following formula (2), number of free protons: 1) Phosphonium salt 3 (a compound represented by the following formula (3), number of free protons: 1) Phosphonium salt 4 (a mixture (semi-neutralized product) of the compound represented by formula (4A) and the compound represented by formula (4B), number of free protons: 1-2) Phosphonium salt 5 (a mixture of the compound represented by formula (5A) and the compound represented by formula (5B) below (total neutralized product), number of free protons: 1-2) Phosphonium salt 6 (a compound represented by the following formula (6), number of free protons: 1) Carboxylate (SYIL-02, manufactured by Sanyo Chemical Industries, Ltd., number of free protons: 1)

[0140] Thickening inhibitors (organic acids containing freeable protons or their neutralized forms): 2-Ethylhexyl acid phosphate (JP-508, manufactured by Johoku Chemical Co., Ltd., number of free protons: 1-2) Tetracosyl acid phosphate (JP-524R, manufactured by Johoku Chemical Co., Ltd., number of free protons: 1-2)

[0141] [ka]

[0142] [ka]

[0143] [ka]

[0144] [ka]

[0145] [ka]

[0146] [ka]

[0147] [ka]

[0148] [ka]

[0149] Note that the compound represented by formula (4A) and the compound represented by formula (5A) are the same. The compound represented by formula (4B) and the compound represented by formula (5B) are the same.

[0150] Curing accelerator (organic acid or its neutralized form that does not contain free-release protons): Phosphonium salt A (a compound represented by the following formula (A), number of free protons: 0) Phosphonium salt B (a compound represented by the following formula (B), number of free protons: 0)

[0151] [ka]

[0152] [ka]

[0153] Curing accelerator (not applicable to organic acids or their neutralized products): Novacure HX-3088 (manufactured by Asahi Kasei Corporation)

[0154] The number of free protons in the above-mentioned organic acid or its neutralized product indicates the number of protons capable of releasing protons with a pKa of 13 or less.

[0155] (Examples 1-13 and Comparative Examples 1-7) (1) Preparation of flux composition The components shown in Tables 1, 3, 5, and 7 below were mixed in the amounts shown in Tables 1, 3, 5, and 7 below. The mixture was stirred at 2000 rpm for 2 minutes using a rotating / revolving mixer (Sinky Co., Ltd. "Awatori Rentaro ARE-310"), and then degassed at 2200 rpm for 3 minutes to obtain a flux composition.

[0156] (evaluation) (1) Properties of the heated product after heating the flux composition at 250°C for 90 seconds A test specimen was obtained by applying 0.05 g of the obtained flux composition to the surface of a copper plate (phosphorus deoxidized copper plate, "C1220" manufactured by Engineering Test Service Co., Ltd., 0.3 mm thick) placed on a glass plate (large slide glass manufactured by Matsunami Glass Co., Ltd., 1.0 mm thick). The obtained test specimen was placed on a hot plate heated to 250°C, with the glass plate side facing outwards. After heating the test specimen for 90 seconds, the properties of the heated flux composition on the 250°C hot plate at 250°C were confirmed by touching it with a bamboo skewer.

[0157] (2) Reaction rate of flux composition at 220°C The obtained flux compositions were subjected to differential scanning calorimetry (DSC) using a differential scanning calorimetry (DSC7020) system (Hitachi High-Tech Science Corporation), heating the flux compositions from 30°C to 360°C at a heating rate of 60°C / min. Using the method described above, the area of ​​the exothermic peak in the temperature range below 220°C (the reaction rate of the flux composition at 220°C) was calculated within 100% of the total area of ​​the exothermic peaks. Furthermore, it was confirmed that the temperature range of the exothermic peaks included 220°C in all examples and comparative examples.

[0158] (3) Wetting properties of solder The obtained flux composition was applied to a substrate (phosphorus deoxidized copper plate, "C1220" manufactured by Engineering Test Services Co., Ltd.) by the dispensing method. Next, solder particles (Sn96.5Ag3.0Cu0.5 solder (melting point: 217°C), particle size 0.5 mm) were placed on the surface of the flux composition layer to form a laminate comprising the substrate, the flux composition layer, and the solder particles. The obtained laminate was heated in a nitrogen atmosphere using a reflow simulator (Core9056a manufactured by Cores Corporation) at a heating rate of 1°C / second from 30°C to 255°C, with a total time above 220°C being 90 seconds, and then cooled to room temperature. After that, the solder particles were observed using a microscope (manufactured by Keyence Corporation), and the major axis (μm) of the solder particles in a plan view was measured. The wetting spreadability of the solder was determined according to the following criteria.

[0159] [Criteria for determining solder wetting spreadability] ○○: Solder particles with a major axis of 800 μm or more ○: Solder particle with a major axis of 700 μm or more and less than 800 μm ×: The longest diameter of the solder particles is less than 700 μm.

[0160] (4) Void suppression of the connecting structure A printed circuit board (material: FR4, Sn42Bi58 solder particles, particle size 0.4 mm, 0.8 mm pitch, 100 electrodes, 10 mm x 10 mm) with solder particles on its surface was prepared. The printed circuit board was placed on the surface of a hot plate with the side opposite to the solder particles facing upwards, and heated at 150°C for 10 minutes to dry. Next, 0.05 g of the freshly prepared flux composition was placed on the surface of the solder particles on the printed circuit board using the dispensing method. A square cover glass (manufactured by Matsunami Glass Co., Ltd.) with dimensions of 18 mm x 18 mm was placed on the surface of the applied flux composition opposite to the printed circuit board to obtain a laminate. The obtained laminate was heated on a hot plate at 250°C for 90 seconds and then cooled to room temperature. After repeating the heating and cooling process three times, the number of voids with a diameter of 100 μm or more was counted using a microscope. The void suppression performance of the connecting structure was judged according to the following criteria.

[0161] [Criteria for determining the void suppression capacity of connecting structures] 〇〇: The number of voids generated is 1 or less. ○: The number of voids generated is between 2 and 3. ×: The number of voids generated is 4 or more.

[0162] The composition and results are shown in Tables 1 to 8 below. In Tables 1, 3, 5, and 7, "Content of organic acids containing freeable protons or their neutralized products in 100% by weight of the flux composition" is expressed as "Content of organic acid additives containing freeable protons in 100% by weight of the flux composition."

[0163] [Table 1]

[0164] [Table 2]

[0165] [Table 3]

[0166] [Table 4]

[0167] [Table 5]

[0168] [Table 6]

[0169] [Table 7]

[0170] [Table 8] [Explanation of Symbols]

[0171] 1…Connection structure 2…First connection target member 2a...First electrode body 2b... Solder particles 2B...Soldering section 3…Second connection target member 3a...Second electrode 4… Resin part 4Xa... Flux composition

Claims

1. A flux composition comprising an epoxy compound, a curing agent, and an organic acid containing a liberable proton or its neutralized form, The curing agent comprises an acid anhydride and a phenol compound, The liberable protons are protons with a pKa of 13 or less, as measured in an aqueous solution at room temperature. The content of the epoxy compound in 100% by weight of the flux composition is 40.0% by weight or more and 70.0% by weight or less. The content of the curing agent in 100% by weight of the flux composition is 30% by weight or more and 60% by weight or less. In 100% by weight of the flux composition, the content of the organic acid containing the liberable proton or its neutralized product is 0.1% by weight or more and 5.0% by weight or less. The properties of the heated flux composition after heating it at 250°C for 90 seconds are that it is solid. The flux composition, when heated in a nitrogen atmosphere at a heating rate of 60°C / min from 30°C to 360°C and differential scanning calorimetry performed, has a temperature range of 220°C in the exothermic peak, and the area of ​​the exothermic peak in the temperature range of 220°C or below accounts for less than 95% of the total area of ​​the exothermic peak.

2. The flux composition according to claim 1, wherein the amount of acid anhydride groups in the flux composition is 16 mol or more and 60 mol or less relative to 100 mol of epoxy groups in the flux composition.

3. The flux composition according to claim 1 or 2, wherein the content of the organic acid containing the freeable proton or its neutralized product is 0.1% by weight or more and 2.0% by weight or less in 100% by weight of the flux composition.

4. The flux composition according to claim 1 or 2, wherein the flux composition is a non-conductive flux composition.

5. The flux composition according to claim 1 or 2, wherein the flux composition is a pre-fill underfill material used in a pre-fill underfill process.

6. The flux composition according to claim 1 or 2, wherein the flux composition is used in contact with a tin-silver-copper alloy solder.

7. Use of the flux composition according to claim 1 or 2 as a pre-fill underfill material used in a pre-fill underfill process.

8. Use of the flux composition according to claim 1 or 2 as a flux on the surface of a tin-silver-copper alloy solder.

9. A first connection target member having a first electrode on its surface, A second connection target member having a second electrode on its surface, The device comprises a resin portion connecting the first connection target member and the second connection target member, The first electrode comprises a first electrode body and solder particles on the surface of the first electrode body. The first electrode body and the second electrode are electrically connected. A connecting structure wherein the material of the resin portion is the flux composition described in claim 1 or 2.

10. A first arrangement step of placing the flux composition on the surface of the solder particles in the first connection target member or on the surface of the second electrode in the second connection target member, using a first connection target member having a first electrode on its surface, wherein the first electrode comprises a first electrode body and solder particles on the surface of the first electrode body, or a second connection target member having a second electrode on its surface, and using the flux composition according to claim 1 or 2, A second arrangement step involves arranging the first connection target member and the second connection target member so that the first electrode and the second electrode face each other. A method for manufacturing a connection structure, comprising the steps of: heating the solder particles and the flux composition to electrically connect the first electrode body and the second electrode, and forming a resin portion connecting the first connection target member and the second connection target member using the flux composition.

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